Re: [RFC PATCH v5 0/3] riscv: Add preliminary custom CSR support

[Alistair Francis]

On Fri, Oct 22, 2021 at 1:13 AM Ruinland Chuan-Tzu Tsai
<ruinland@andestech.com> wrote:
>
> Hi Alistair, Bin and all :
>
> Sorry for bumping this stale topic.
> As our last discussion, I have removed Kconfigs and meson options.
> The custom CSR logic is in-built by default and whether a custom CSR
> is presented on the accessing hart will be checked at runtime.

No worries!

This looks great! I had a look through this and I think we are almost
there. I left a few comments, but otherwise I think we are close.

Let's see if anyone else has any comments. Otherwise can you run
checkpatch on each patch and then send a PATCH series (not an RFC) in
a week or so and we can go from there.

>
> Changes from V4 :
> Remove Kconfigs and meson options.
> Make custom CSR handling logic self-contained.
> Use g_hash_table_new instead of g_hash_table_new_full.
>
> The performance slowdown could be easily tested with a simple program
> running on linux-user mode :
>
> /* test_csr.c */
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/time.h>
>
> int main (int ac, char *av[]) {
>    struct  timeval start;
>    struct  timeval end;
>    gettimeofday(&start,NULL);
>    unsigned int loop_n = 999999 ;
>    unsigned char i;
>    unsigned char o;
>    do {
>        for(i=0; i<32; i++) {
>        #if defined(FCSR)
>        __asm__("csrw fcsr, %0;"::"r"(i));
>        __asm__("csrr %0, fcsr;":"=r"(o));
>        #elif defined(UITB)
>        __asm__("csrw 0x800, %0;"::"r"(i));
>        __asm__("csrr %0, 0x800;":"=r"(o));
>        #endif
>        }
>        --loop_n;
>    } while (loop_n > 0);
>    gettimeofday(&end,NULL);
>    unsigned long diff = 1000000 *
> (end.tv_sec-start.tv_sec)+end.tv_usec-start.tv_usec;
>    printf("%f\n", (double)(diff)/1000000);
>    return 0;
> }
>
> $ riscv64-linux-gnu-gcc -static -DUITB ./test_csr.c -o ./u
> $ riscv64-linux-gnu-gcc -static -DFCSR ./test_csr.c -o ./f
> $ qemu-riscv64 ./{u,f}

Do you have the results?

Alistair

>
> Cordially yours,
> Ruinland Chuan-Tzu Tsai
>
> Ruinland Chuan-Tzu Tsai (3):
>   riscv: Adding Andes A25 and AX25 cpu models
>   riscv: Introduce custom CSR hooks to riscv_csrrw()
>   riscv: Enable custom CSR support for Andes AX25 and A25 CPUs
>
>  target/riscv/andes_cpu_bits.h  | 129 +++++++++++++++++++++++
>  target/riscv/cpu.c             |  39 +++++++
>  target/riscv/cpu.h             |  15 ++-
>  target/riscv/csr.c             |  38 +++++--
>  target/riscv/csr_andes.c       | 183 +++++++++++++++++++++++++++++++++
>  target/riscv/custom_csr_defs.h |   8 ++
>  target/riscv/meson.build       |   1 +
>  7 files changed, 404 insertions(+), 9 deletions(-)
>  create mode 100644 target/riscv/andes_cpu_bits.h
>  create mode 100644 target/riscv/csr_andes.c
>  create mode 100644 target/riscv/custom_csr_defs.h
>
> --
> 2.25.1
>